Brian Jackson

Associate Professor of Physics at Boise State University

  • About
  • Research
    • CV
    • Joining the Boise State Planetary Science Research Group
    • Research Experiences for Undergrads
    • Ultra-short-period planet database
    • The Short Period Planets Group — S(u)PerP(i)G
    • Google Scholar Page
    • Code
  • Teaching
  • Press
  • Extracurricular Activities
    • Field Trips
      • Bruneau Sand Dunes – 2022 Jun 29
  • Public Outreach
    • Boise State’s Astronomical Observatory
    • Central Idaho Dark Sky Reserve STEM Network

Hot Planets and Heavy-Metal Stars

Posted by admin on April 11, 2017
Posted in: BSU Journal Club. Tagged: close-in planets, exoplanets, hot jupiters, Kepler mission, ultra-short-period planets.

Artist’s conception of the ultra-short-period planet Kepler-78 b, discovered by Sanchis-Ojeda and colleagues in 2013.

An eyebrow-raising paper emerged recently from Prof. Josh Winn and colleagues about a type of planet near and dear to my heart, ultra-short-period planets, or USPs for short.

These planets are roughly the size of Earth and probably rocky but are hundreds of times closer to their host star than the Earth is to the Sun. These planets are so hot some have melted daysides and others are evaporating. Because they’re so much closer to their stars, ultra-short-period planets zip around their stars in just hours – hence the clunky name.

Our group, along with others, has suggested USPs might be the remnants of hot Jupiters (gas-giant planets close to their stars) that had their atmospheres ripped off. If so, we’d expect systems hosting USPs to resemble systems hosting hot Jupiters.

One distinctive feature of stars with hot Jupiters is that they have more iron (Fe) and other heavy elements in their atmospheres. Astronomers call the amount of heavy elements (“metals”)  stellar metallicity. Hot-Jupiter host stars are heavy in metals probably because planets form from the same materials as the star and big planets need large amounts of metals to form. The same trend doesn’t seem to hold for small, roughly Earth-sized planets, though – small planets don’t seem to be as picky. So, if USPs are hot Jupiters that lost their atmospheres, their stars should also be metal-rich.

Figure 4 from Winn et al. (2017), showing the distribution of stellar metallicities for USP-hosting stars (red), hot Jupiter-hosting stars (orange), and stars hosting small but slightly longer period planets (blue).

But the recent paper from Winn and colleagues throws this origin story for USPs into doubt. In their study, they looked at metallicities for stars hosting USPs, stars hosting hot Jupiters, and those hosting small planets a bit farther out than USPs, all discovered by the Kepler Mission. The figure at left shows their results.

As expected, the orange curve for hot Jupiter hosts peaks toward higher metallicity (that is, toward bigger [Fe/H]-values), and if USPs are former hot Jupiters, the red histogram should look like the orange one.

Instead, it looks a lot like the blue one for smaller, farther out planets. This result suggests that USPs are just like their longer-period cousins – planets that have always been small, just with very short periods.

What to make of this? There’s some statistical wiggle room, allowing some, but not all, USPs to have been hot Jupiters, but Winn’s analysis says no more than 46%. It’s also possible that the boundaries between what Winn calls “hot Jupiters” and what he calls “hot small planets” could be refined by additional analysis, shifting the orange curve down a bit (or maybe shifting the blue curve up).

But the chances that USPs experienced a dramatic and brutal origin are a little slimmer now. Maybe that’s a good thing – it says the universe might be a little bit less violent than we thought.

Posts navigation

← Pony Up Campaign: Eclipse Shades Ordered
Solar Eclipse – 2017 Aug 21 →
  • Twitter: decaelus

    Brian Jackson
    • Learn how to save the dark (https://t.co/CqYzD5o2Xh at @BroncoPhysics First Friday Astronomy event this Fri (Feb 3… https://t.co/8B3Set3tW0 10:49:28 2023 Jan 30
    • RT @decaelus: Get paid to live in the beautiful @Idahodarksky next summer - https://t.co/sgoWb9PrpK. E-mail me directly with any question… 05:08:24 2023 Jan 7
    • Get paid to live in the beautiful @Idahodarksky next summer - https://t.co/sgoWb9PrpK. E-mail me directly with an… https://t.co/B9V7FwtQxx 02:47:26 2022 Dec 19
    @decaelus
  • Recent Posts

    • Saving the Dark
    • Introduction to CIDSRSN – 2023 Jan 27
    • Astronomy Research Group Meeting – 2023 Jan 26
    • Astronomy Research Group Meeting – 2023 Jan 19
    • Dust in the Wind – Presentation at College of Idaho – 2023 Feb 14
  • Archives

    • January 2023
    • December 2022
    • November 2022
    • October 2022
    • September 2022
    • August 2022
    • July 2022
    • June 2022
    • May 2022
    • April 2022
    • March 2022
    • February 2022
    • January 2022
    • December 2021
    • November 2021
    • October 2021
    • September 2021
    • August 2021
    • July 2021
    • June 2021
    • May 2021
    • April 2021
    • March 2021
    • February 2021
    • January 2021
    • December 2020
    • November 2020
    • October 2020
    • September 2020
    • August 2020
    • July 2020
    • June 2020
    • May 2020
    • April 2020
    • March 2020
    • February 2020
    • January 2020
    • December 2019
    • November 2019
    • October 2019
    • September 2019
    • August 2019
    • July 2019
    • June 2019
    • May 2019
    • April 2019
    • March 2019
    • February 2019
    • January 2019
    • December 2018
    • November 2018
    • October 2018
    • September 2018
    • August 2018
    • July 2018
    • June 2018
    • May 2018
    • April 2018
    • March 2018
    • February 2018
    • January 2018
    • December 2017
    • November 2017
    • October 2017
    • September 2017
    • August 2017
    • July 2017
    • June 2017
    • May 2017
    • April 2017
    • March 2017
    • February 2017
    • January 2017
    • December 2016
    • November 2016
    • October 2016
    • September 2016
    • August 2016
    • July 2016
    • June 2016
    • May 2016
    • April 2016
    • March 2016
    • February 2016
    • January 2016
    • December 2015
    • November 2015
    • October 2015
    • September 2015
    • August 2015
    • July 2015
    • June 2015
    • May 2015
    • April 2015
    • March 2015
    • February 2015
    • January 2015
    • December 2014
    • November 2014
    • October 2014
    • September 2014
    • August 2014
    • July 2014
    • June 2014
    • May 2014
    • April 2014
    • March 2014
    • February 2014
    • January 2014
    • December 2013
    • November 2013
    • October 2013
    • September 2013
    • August 2013
    • July 2013
Proudly powered by WordPress Theme: Parament by Automattic.